Brake mechanisms for vehicles and, in particular, heavy duty trucks, typically include a spring brake actuator. A spring brake actuator is typically held in a caged or compressed state for storage and shipping. Further, such actuators are typically installed and adjusted while in the compressed state. A retaining mechanism is required to hold a spring actuator in its compressed state because it would be difficult for a human operator to manually compress a spring brake actuator. Rather, machines utilizing compressed air are required to exert several thousand pounds of force on the opposite ends of a spring in a spring brake actuator to compress it. While the spring is held in a compressed state, a retaining mechanism is installed to hold the spring brake actuator in its compressed state. After storage, shipment and/or installation, the retaining mechanism is removed. The retaining mechanism holds the spring brake actuator in its compressed state, while the operator installs the spring brake actuator and adjusts the brake mechanism before removing the retaining apparatus.
The prior art is illustrated in FIG. 1, wherein there is shown a clip or key 10' adapted to be inserted into a spring support 14 to maintain the spring identified by the numeral 60 in a compressed state, as shown in FIG. 3B. The clip 10' includes an enlarged head 20', a shank 16' extending downwardly therefrom and a pair of tabs 18a' and 18b' extending out from the shank 16' in perpendicular relation thereto. The prior art clip 10' is inserted into and engages the spring support 14, which compresses as shown in FIGS. 3B and 3C, a circular shaped base and a housing 42 for retaining therebetween a spring brake actuator in a compressed or caged state. In particular, the clip 10' is inserted through a release boss 50 and an opening 52 of a collar 46. As particular shown in FIG. 3C, the tabs fit through a pair of slots 54a and b. Thereafter, the clip 10' is rotated, whereby the tabs 18a' and 18b' engage the lower surface of the lip 48, thereby, retaining the housing 42 and the base 40 at a fixed distance therebetween and holding the spring 60 in its compressed state. Examination of FIG. 1 indicates that the spacing between the base 40 and the housing 42 is fixedly set by the distance indicated by the letter L between the top of each of the tabs 18a' and 18b' and the corresponding one of the straight edges 21a' and 21b'. The straight edges 21a' and 21b' are disposed perpendicular to the shank 16' whereby there is no adjustment in the spacing between the housing 42 and the base 40. Such a construction presents a problem in that the clip 10' and the spring 60 are typically manufactured with some tolerances. As a result of these tolerances, the actual dimension from one end to the other of the spring 60 in its compressed state, will vary. Likewise, the spacing between the housing 42 and the base 40 will vary to some degree because the prior art clip 10' and its distance L will have some tolerance.
In the installation of the spring 60 into its brake mechanism, it is desirable to compress the spring 60 to a point where the spring 60 may not be further compressed. A totally compressed spring 60 is relatively easy to install and adjust. However, with the clip 10' of the prior art, it is necessary to set the distance L to take into account the manufacturing tolerances with which the clip 10' and the spring 60 are manufactured. In practice, the distance L is set such that in most instances that the spring brake actuator is not totally compressed, thus increasing the difficulty of installation and adjustment of the spring 60.
U.S. Pat. Nos. 4,657,462 and 2,588,951 are examples of prior art fasteners for retaining two or more plates together and including a clip and a spring. First, such prior art is not concerned with maintaining the included spring in a fully compressed state, much less teach that the mechanism for providing a variable adjustment of the distance between the ends of a spring such that the spring is held by the fastener in a fully compressed state.